The present invention relates to vapor permeation curable coatings and more particularly for such coatings specially adapted for reaction injection molded parts.
Reaction Injection Moldings (RIM) are urethanes basically consisting of a polyol and a polyisocyanate, usually with an extender (eg. a glycol or a diamine), optionally with a blowing agent (eg. air), optional reinforcing material (eg. glass, mica, etc.), wetting agents, and the like, which materials are high pressure injected through a mixing head into a pre-heated mold with usual post-molding baking thereafter applied. RIM urethanes can range from low modulus to very high modulus material parts, foamed on the interior but with a smooth surface. RIM urethanes are capable of being made into very large one-piece parts which are very light in weight. Typical present-day uses of RIM parts include automobile parts (eg. bumpers, air deflectors, fenders, front ends, etc.), business machine housings, ski boots, office furniture, and a very wide variety of products. Further information on RIM urethanes can be found in the following references: "RIM urethanes coming on strong", Product Engineering, Morgan-Grampian Publishing Co. (June 1978); "Reaction injection molding", Modern Plastics Encyclopedia 1980-1981, pages 379-382, McGraw Hill, Inc.; "RIM: ready to move beyond Detroit", Purchasing, Cahners Publishing Company (Dec. 6, 1977); "Improving RIM technology multiplies the options", Modern Plastics, McGraw Hill, Inc., New York (1978); and "RIM Urethanes", Plastics World, Cahners Publishing Co. (May, 1981).
Especially for the automotive industry, such as for bumpers, since RIM urethane automotive parts are designed to flex on impact, such parts are painted with flexible paints. Existing commercial paints include, for example, melaminecured aliphatic urethane baking enamels, non-urethane melamine-acrylic enamels, 2-pack heat-cured urethanes, and urethane lacquers. Heating of these coatings for cure often damages the RIM urethane part. Such paints must possess a great deal of flexibility while maintaining adequate adhesion to the very smooth surface of the RIM part. Further, the coating must possess good solvent resistance, especially for an automobile bumper which is exposed to gasoline, for example, water and humidity resistance, salt-spray resistance, resistance to discoloration in sunlight, and additional performance requirements.
The coatings of the present invention not only meet or exceed performance requirements for RIM parts and especially for automobile parts such as bumpers, but are cured rapidly at room temperature.